Definition 3.4 (Mutual information[1]}) 

Let \((X,Y)\)  be a pair of random variables defined over the discrete space \(\mathcal {X}\times \mathcal {Y}\) . The Mutual information (MI) of \(X\)  and \(Y\)  is given as:
\(MI(X,Y)=\sum \limits _{x\in \mathcal {X}}\sum \limits _{y\in \mathcal {Y}}\mu (x,y)\log \frac{\mu (x,y)}{p_{\mathcal {X}}(x)p_{\mathcal {Y}}(y)}\) 
